The AD-box always sends all samples to the PC, and the PC processes all samples. If for some reason, ActiView cannot keep up with the incoming data-stream, an error is detected and the program stops with a popup message. So, the data in the BDF file always contains ALL samples, you can be 100% sure that there are no gaps.

Looking at the Data coming out of Downsample-5th.vi, is it trickling out sample after sample or does it come in some sort of frames, i.e. chunks of data?

The way I understand it is, for example, when averaging is computed relative to the trigger: the trigger word is found and buffering starts, and by that I mean the samples that are coming in are buffered in a matrix, one sample after the other, until the trigger starts again, and then the word if found again, and that is the second run for buffering which gets averaged with the ones before.

The 2D output arrays from Downtsample-5th.vi have a constant number of rows (number of channels, dependent on the speedmode), and a variable number of columns (successive samples, amount of samples in an array depends on the value of the "display block size", which is constantly adjusted according to the backlog)

The average buffer starts top fill with samples after a trigger is detected. The buffer fills until the "sweep length" is reached (new triggers are ignored until during the sweep).